ZR36060PQC datasheet(25/46 Pages) ETC

25 / 46 page

Integrated JPEG CODEC

system stops the video using the PVALID input. This may be

useful, for example, when decompressing still pictures.

When the code interface operates in slave mode (see Figure 33)

the scenario is almost identical. The main difference is that

CBUSY is now an output of the ZR36060, and it is used to

indicate that the code FIFO is “nearly full”, thus the host must

momentarily stop writing code until CBUSY indicates that the

FIFO occupancy is below its threshold.

6.6 Compression and Decompression Modes

The ZR36060 has one decompression mode (called simply

decompression), and four compression modes:

• Compression Pass

• Statistical Compression Pass

• Auto Two-Pass Compression

• Tables-Only Compression Pass

The following sections describe these modes.

6.7 Compression Pass

When the ZR36060 is in the IDLE state, and after the correct ini-

tialization has been done by the host (loading parameters and/or

tables), it waits for a command (assertion of START) to start

compressing. RTBSY is not asserted at this time. Once the

ZR36060 senses an active (low) START, it checks the level of

FRAME, and then, if FRAME is active (Figure 34), the ZR36060

starts compressing the next odd field (i.e., at the next odd

VSYNC).

Note: If FRAME is maintained active, and consequently it will be

detected active every time START is sampled active, the

ZR36060 will compress only the odd fields. This is a convenient

method for implementing field decimation.

If FRAME is not active when START is sampled (Figure 35), the

ZR36060 always starts compressing the next field (i.e., at the

next VSYNC).

The VSYNC edge used by the ZR36060 to make the decision on

the ‘next’ field is configurable with the FIVedge parameter

(leading or trailing edge).

During IDLE, CBUSY (if it is configured as output, in code slave

mode) is active, preventing the host controller from reading

code, since the code FIFO buffer is empty. Once the compres-

sion process starts CBUSY is released and the host controller is

expected to read the code. If the ZR36060 is the master of the

code bus it drives out the code only after the compression

process starts (the active area begins).

When the compression of the field is not stopped because of an

interrupt request targeted to the host (JIRQ assertion), then upon

completion the ZR36060 asserts the END signal and returns to

the IDLE state, looking again at START and FRAME. Note that

it does not matter if the host controller continuously asserts

START (and/or FRAME) or if it only asserts START (and/or

FRAME) after the ZR36060 asserts END. The reason is that the

ZR36060 interrogates START only when it is in the IDLE state.

See Figure 36.

Figure 32. Data Flow in Decompression, Code Master

Video Bus

Strip Memory

JPEG Codec

CODE FIFO

CODE Bus

RTBSY

CBUSY

CCS

Figure 33. Data Flow in Decompression, Code Slave

Video Bus

Strip Memory

JPEG Codec

CODE FIFO

CODE Bus

RTBSY

CBUSY

Figure 34. Compression with START and FRAME

continuously asserted

START

FRAME

state

VSYNC

IDLE

END

EVEN

ODD

EVEN

ODD

WAIT

ACTIVE

CMP

IDLE

WAIT

ACTIVE

CMP

IDLE

2 Processed Fields

Figure 35. Compression with continuous START asserted

and FRAME Deasserted

START

FRAME

state

VSYNC

IDLE

END

WAIT

ACTIVE

CMP

IDLE

3 Processed Fields

CMP

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